Endoluminal repair or exclusion of aneurysms, such as in the aorta, has been performed in recent years. Endoluminal aortic aneurysm exclusion can correct a life-threatening disease in a minimally invasive manner in order to effectuate a patient's quick and complete recovery. Various vascular grafts exist that have been used to exclude aortic aneurysms.
The aorta is the largest artery in the body and is responsible for delivering blood from the heart to the organs of the body. The aorta includes the thoracic aorta, which arises from the left ventricle of the heart, passes upward, bends over and passes down towards the thorax, and the abdominal aorta which passes through the thorax and through the abdomen to about the level of the fourth lumbar vertebra, where it divides into the two common iliac arteries. The thoracic aorta is divided into the (i) ascending aorta, which arises from the left ventricle of the heart, (ii) the aorta arch, which arches from the ascending aorta and (iii) the descending aorta which descends from the aorta arch towards the abdominal aortic.
A thoracic aortic aneurysm (“TAA”) is a widening, bulge, or ballooning out of a portion of the thoracic aorta, usually at a weak spot in the aortic wall. If left untreated, the aneurysm may progressively expand until the vessel dissects or ruptures. This may lead to severe and even fatal hemorrhaging. Factors leading to thoracic aorta aneurysms include hardening of the arteries (atherosclerosis), hypertension, congenital disorders such as Marfan's syndrome, trauma, or less commonly syphilis. Thoracic aorta aneurysms occur in the ascending aorta about 25% of the time, the aortic arch about 25% of the time and in the descending aorta about 50% of the time.
Treatment of thoracic aorta aneurysms depends upon the location of the aneurysm. For aneurysms in the ascending aorta or aortic arch, surgery is typically required to replace the aorta with an artificial vessel. This surgical procedure typically requires exposure of the aorta and the use of a heart-lung machine. If the aortic arch is involved, a specialized technique called “circulatory arrest” (i.e., a period without blood circulation while on life support) may be necessary. For aneurysms in the descending aorta, the vessel may also be replaced with an artificial vessel through surgery. In some circumstances, an endoluminal vascular graft may be used eliminating the need for open surgery.
Straight tube grafts have been used in the infrarenal abdominal aorta to exclude an aneurysmal sac from the blood stream, thereby resulting in the weakened aortic wall being protected by graft material. These straight tube grafts were initially unsupported; they employed stents at their proximal and distal ends to anchor the proximal and distal ends of the graft to the healthy portions of the aorta thereby leaving a midsection of the graft or prosthesis that did not have any internal support. Although this type of graft at first appeared to correct the aortic aneurysm, it met with many failures. The unsupported nature of its midsection allowed the graft to migrate distally as well as exhibit significant proximal leakage due to the enlargement of the aorta without adaptation of the graft, such as enlargement of the graft, to accommodate the change in diameter of the aorta.
Technical improvements in stent design led to “self-expanding” stents. In addition, later improvements produced Nitinol stents which have a “memory” capable of expanding to a predetermined size. Graft designers began to develop bifurcated grafts having limbs which extended into the iliac arteries. The development of bifurcated grafts allowed for the treatment of more complex aneurysms.
Many bifurcated grafts are of a two-piece or modular design. The two-piece designs often require the insertion of a contralateral limb through or a separate access site. These types of grafts are complex to deploy and have the potential for leakage at the connection site of the two limbs of the graft.
Endoluminal implantation is a common technique for implanting vascular grafts. Typically, this procedure involves percutaneously inserting a vascular graft or prosthesis by using a delivery catheter. This process eliminates the need for major surgical intervention, thereby decreasing the risks associated with vascular and arterial surgery.